Selective bifunctional multigradient multimetallic catalyst

ABSTRACT

A novel catalyst and the use thereof in a reforming process are disclosed. The catalyst comprises a refractory inorganic oxide, uniform platinum-group metal, uniform Group IVA (IUPAC 14) metal and surface-layer lanthanide-series metal. The catalyst is particularly suitable for the reforming of a hydrocarbon feedstock to obtain an aromatics-rich product.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of application Ser.No. 09/312,869 filed May 17, 1999, which is a continuation-in-part ofapplication Ser. No. 08/762,620 filed Dec. 9, 1996, and now U.S. Pat.No. 6,013,173.

FIELD OF THE INVENTION

[0002] This invention relates to an improved catalyst for the conversionof hydrocarbons, and more specifically for the catalytic reforming ofgasoline-range hydrocarbons.

BACKGROUND OF THE INVENTION

[0003] The subject of the present invention is a novel dual-functioncatalyst, characterized by a multimetallic, multigradient combination ofthree or more metal components in specified concentrations on thefinished catalyst, and its use in hydrocarbon conversion. Catalystshaving both a hydrogenation-dehydrogenation function and a crackingfunction are used widely in many applications, particularly in thepetroleum and petrochemical industry, to accelerate a wide spectrum ofhydrocarbon-conversion reactions. The cracking function generallyrelates to an acid-action material of the porous, adsorptive,refractory-oxide type which is typically utilized as the support orcarrier for a heavy-metal component, such as the Group VIII (IUPAC 8-10)metals, which primarily contribute the hydrogenation-dehydrogenationfunction. Other metals in combined or elemental form can influence oneor both of the cracking and hydrogenation-dehydrogenation functions.

[0004] In another aspect, the present invention comprehends improvedprocesses that emanate from the use of the novel catalyst. Thesedual-function catalysts are used to accelerate a wide variety ofhydrocarbon-conversion reactions such as dehydrogenation, hydrogenation,hydrocracking, hydrogenolysis, isomerization, desulfurization,cyclization, alkylation, polymerization, cracking, andhydroisomerization. In a specific aspect, an improved reforming processutilizes the subject catalyst to increase selectivity to gasoline andaromatics products.

[0005] Catalytic reforming involves a number of competing processes orreaction sequences. These include dehydrogenation of cyclohexanes toaromatics, dehydroisomerization of alkylcyclopentanes to aromatics,dehydrocyclization of an acyclic hydrocarbon to aromatics, hydrocrackingof paraffins to light products boiling outside the gasoline range,dealkylation of alkylbenzenes and isomerization of paraffins. Some ofthe reactions occurring during reforming, such as hydrocracking whichproduces light paraffin gases, have a deleterious effect on the yield ofproducts boiling in the gasoline range. Process improvements incatalytic reforming thus are targeted toward enhancing those reactionseffecting a higher yield of the gasoline fraction at a given octanenumber.

[0006] It is of critical importance that a dual-function catalystexhibit the capability both to initially perform its specified functionsefficiently and to perform them satisfactorily for prolonged periods oftime. The parameters used in the art to measure how well a particularcatalyst performs its intended functions in a particular hydrocarbonreaction environment are activity, selectivity and stability. In areforming environment, these parameters are defined as follows:

[0007] (1) Activity is a measure of the ability of the catalyst toconvert hydrocarbon reactants to products at a designated severitylevel, with severity level representing a combination of reactionconditions: temperature, pressure, contact time, and hydrogen partialpressure. Activity typically is designated as the octane number of thepentanes and heavier (“C₅+”) product stream from a given feedstock at agiven severity level, or conversely as the temperature required toachieve a given octane number.

[0008] (2) Selectivity refers to the percentage yield of petrochemicalaromatics or C₅+ gasoline product from a given feedstock at a particularactivity level.

[0009] (3) Stability refers to the rate of change of activity orselectivity per unit of time or of feedstock processed. Activitystability generally is measured as the rate of change of operatingtemperature per unit of time or of feedstock to achieve a given C₅+product octane, with a lower rate of temperature change corresponding tobetter activity stability, since catalytic reforming units typicallyoperate at relatively constant product octane. Selectivity stability ismeasured as the rate of decrease of C₅+ product or aromatics yield perunit of time or of feedstock.

[0010] Programs to improve performance of reforming catalysts are beingstimulated by the reformulation of gasoline, following upon widespreadremoval of lead antiknock additive, in order to reduce harmful vehicleemissions. Gasoline-upgrading processes such as catalytic reforming mustoperate at higher efficiency with greater flexibility in order to meetthese changing requirements. Catalyst selectivity is becoming ever moreimportant to tailor gasoline components to these needs while avoidinglosses to lower-value products. The major problem facing workers in thisarea of the art, therefore, is to develop more selective catalysts whilemaintaining effective catalyst activity and stability.

[0011] The art teaches a variety of multimetallic catalysts for thecatalytic reforming of naphtha feedstocks. Most of these comprisecombinations of platinum-group metals with rhenium and/or Group IVA(IUPAC 14) metals.

[0012] U.S. Pat. No. 3,915,845 (Antos) discloses hydrocarbon conversionwith a catalyst comprising a platinum-group metal, Group IVA metal,halogen and lanthanide in an atomic ratio to platinum-group metal of 0.1to 1.25. The preferred lanthanides are lanthanum, cerium, and especiallyneodymium which was exemplified in Antos. U.S. Pat. No. 4,039,477(Engelhard et al.) discloses a catalyst for the catalytic hydrotreatmentof hydrocarbons comprising a refractory metal oxide, platinum-groupmetal, tin and at least one metal from yttrium, thorium, uranium,praseodymium, cerium, lanthanum, neodymium, samarium, dysprosium andgadolinium with favorable results being observed at relatively lowratios of the latter metals to platinum. U.S. Pat. No. 5,665,223(Bogdan) teaches a catalytic composite comprising a refractory inorganicoxide, Group IVA (IUPAC 14) metal, platinum-group metal and europiumwherein the atomic ratio of europium to platinum-group metal is at leastabout 1.3.

[0013] Moreover, U.S. Pat. No. 5,102,850 (Sanchez) discloses ceriumdioxide and a catalytically effective amount of platinum, which isimpregnated in a radial gradient on an automotive exhaust catalyst. Thisoxidized catalyst teaches a dual gradient of both platinum and cerium,which is unlike the present invention having uniform platinum and whichis used in a different catalytic process.

SUMMARY OF THE INVENTION

[0014] It is an object of the invention to provide a novel catalyst forhydrocarbon conversion. A corollary object of the invention is toprovide a reforming process having improved activity and selectivity forthe production of gasoline and/or aromatics.

[0015] The invention originates from the discovery that a catalystcontaining platinum, tin and cerium on chlorided alumina shows afavorable ratio of aromatization to cracking in a reforming reaction.

[0016] A broad embodiment of the present invention is a catalystcomprising a refractory inorganic oxide and a multimetallic,multigradient metal component comprising a platinum-group metalcomponent, a Group IVA (IUPAC 14) metal component, and a surface-layerlanthanide-series metal component. The platinum-group-metal generally ispresent in the catalyst in an amount of about 0.01 to 2 mass-% on anelemental basis of component, the Group IVA (IUPAC 14) metal componentin an amount of about 0.01 to 5 mass-% on an elemental basis, and thesurface-layer lanthanide-series-metal component in an amount of about0.05 to 5 mass-% on an elemental basis. The atomic ratio of thelanthanide metal to platinum-group metal preferably is at least about1.5, more preferably at least about 2. The catalyst optimally alsocomprises a halogen, especially chlorine. In preferred embodiments therefractory inorganic oxide is alumina, the platinum-group metal isplatinum, the Group IVA (IUPAC 14) metal is tin, and thelanthanide-series metal is cerium. A highly preferred catalyst consistsessentially of platinum, tin and cerium on a halogenated aluminasupport.

[0017] In another aspect, the invention is a process for the conversionof a hydrocarbon feedstock to obtain an aromatics-enhanced productutilizing a catalyst comprising a refractory inorganic oxide and amultimetallic, multigradient metal component comprising a platinum-groupmetal component, a Group IVA (IUPAC 14) metal component, and asurface-layer lanthanide-series metal component. Preferably thehydrocarbon conversion is catalytic reforming of a naphtha feedstock,utilizing the catalyst of the invention to increase the yield ofgasoline and/or aromatics in the product.

[0018] These as well as other objects and embodiments will becomeevident from the following more detailed description of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 illustrates cerium distribution in catalyst particles ofthe invention in comparison to distribution in particles of the knownart.

[0020]FIG. 2 shows conversion of paraffins+naphthenes as a function ofcatalyst temperature when reforming naphtha using catalysts of theinvention and of the known art.

[0021]FIG. 3 shows C₅+ product yields as a function of conversion whenreforming naphtha consistent with the results of FIG. 2 for catalysts ofthe invention and of the known art.

[0022]FIG. 4 illustrates cerium distribution in catalyst particles ofthe invention in comparison to distribution in particles of the knownart.

[0023]FIG. 5 illustrates cerium and tin distribution in a cerium-tinreforming composite of the invention.

[0024]FIG. 6 illustrates lanthanum and tin distribution in alanthanum-tin reforming composite of the invention.

[0025]FIG. 7 shows conversion of heptene as a function of space velocityfor the composites of FIGS. 5 and 6 and a catalyst of the known art.

[0026]FIG. 8 shows selectivity to naphthenes and aromatics as a functionof conversion of heptene consistent with the results of FIG. 7 forcomposites of the invention and of the known art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] A broad embodiment of the present invention, therefore, is acatalyst comprising a refractory inorganic-oxide support, aplatinum-group metal, at least one metal of Group IVA (IUPAC 14) of thePeriodic Table [See Cotton and Wilkinson, Advanced Inorganic Chemistry,John Wiley & Sons (Fifth Edition, 1988)] and a lanthanide-series metal,preferably in combination with a halogen.

[0028] The refractory support utilized in the present invention usuallyis a porous, adsorptive, high-surface area support having a surface areaof about 25 to about 500 m²/g. The porous carrier material should alsobe uniform in composition and relatively refractory to the conditionsutilized in the hydrocarbon conversion process. By the terms “uniform incomposition” it is meant that the support be unlayered, has noconcentration gradients of the species inherent to its composition, andis completely homogeneous in composition. Thus, if the support is amixture of two or more refractory materials, the relative amounts ofthese materials will be constant and uniform throughout the entiresupport. Included within the scope of the present invention carrier arematerials which have traditionally been utilized in dual-functionhydrocarbon conversion catalysts such as:

[0029] (1) refractory inorganic oxides such as alumina, magnesia,titania, zirconia, chromia, zinc oxide, thoria, boria, silica-alumina,silica-magnesia, chromia-alumina, alumina-boria, silica-zirconia, etc.;

[0030] (2) ceramics, porcelain, bauxite;

[0031] (3) silica or silica gel, silicon carbide, clays and silicateswhich are synthetically prepared or naturally occurring, which may ormay not be acid treated, for example attapulgus clay, diatomaceousearth, fuller's earth, kaolin, or kieselguhr;

[0032] (4) crystalline zeolitic aluminosilicates, such as X-zeolite,Y-zeolite, mordenite, □-zeolite, □-zeolite or L-zeolite, either inhydrogen form or preferably in nonacidic form with one or more alkalimetals occupying the cationic exchangeable sites;

[0033] (5) non-zeolitic molecular sieves, such as aluminophosphates orsilico-alumino-phosphates; and

[0034] (6) combinations of two or more materials from one or more ofthese groups.

[0035] Preferably the refractory support comprises one or more inorganicoxides, with the preferred refractory inorganic oxide for use in thepresent invention being alumina. Suitable alumina materials are thecrystalline aluminas known as the gamma-, eta-, and theta-alumina, withgamma- or eta-alumina giving best results. The preferred refractoryinorganic oxide will have an apparent bulk density of about 0.3 to about1.0 g/cc and surface area characteristics such that the average porediameter is about 20 to 300 angstroms, the pore volume is about 0.1 toabout 1 cc/g, and the surface area is about 100 to about 500 m²/g.

[0036] Considering that alumina is the preferred refractory inorganicoxide, a particularly preferred alumina is that which has beencharacterized in U.S. Pat. Nos. 3,852,190 and 4,012,313 as a by-productfrom a Ziegler higher alcohol synthesis reaction as described inZiegler's U.S. Pat. No. 2,892,858, hereinafter referred to as a “Ziegleralumina”. Ziegler alumina is presently available from the Vista ChemicalCompany under the trademark “Catapal” or from Condea Chemie GmbH underthe trademark “Pural,” and will be available from ALCOA under thetrademark “HiQ-20.” This high-purity pseudoboehmite, after calcinationat a high temperature, has been shown to yield a gamma-alumina ofextremely high purity.

[0037] The alumina powder can be formed into particles of any desiredshape or type of carrier material known to those skilled in the art suchas spheres, rods, pills, pellets, tablets, granules, extrudates, andlike forms by methods well known to the practitioners of the catalystmaterial forming art. Such particles preferably have at least oneregular dimension, usually a circular cross-section and referred toherein as a “diameter,” of between about 0.7 and about 3.5 mm.

[0038] The preferred form of the present catalyst support is a sphericalparticle, with a preferred diameter of between about 0.7 and about 3.5mm. Alumina spheres may be continuously manufactured by the well knownoil-drop method which comprises: forming an alumina hydrosol by any ofthe techniques taught in the art and preferably by reacting aluminummetal with hydrochloric acid; combining the resulting hydrosol with asuitable gelling agent; and dropping the resultant mixture into an oilbath maintained at elevated temperatures. The droplets of the mixtureremain in the oil bath until they set and form hydrogel spheres. Thespheres are then continuously withdrawn from the oil bath and typicallysubjected to specific aging and drying treatments in oil and anammoniacal solution to further improve their physical characteristics.The resulting aged and gelled particles are then washed and dried at arelatively low temperature of about 1500 to about 205° C. and subjectedto a calcination procedure at a temperature of about 450° to about 700°C. for a period of about 1 to about 20 hours. This treatment effectsconversion of the alumina hydrogel to the corresponding crystallinegamma-alumina. U.S. Pat. No. 2,620,314 provides additional details andis incorporated herein by reference thereto.

[0039] An alternative form of carrier material is a cylindricalextrudate, preferably prepared by mixing the alumina powder with waterand suitable peptizing agents such as HCl until an extrudable dough isformed. The amount of water added to form the dough is typicallysufficient to give a loss on ignition (LOI) at 500° C. of about 45 to 65mass-%, with a value of 55 mass-% being preferred. The acid additionrate is generally sufficient to provide 2 to 7 mass-% of thevolatile-free alumina powder used in the mix, with a value of 3 to 4mass-% being preferred. The resulting dough is extruded through asuitably sized die to form extrudate particles. These particles are thendried at a temperature of about 260° to about 427° C. for a period ofabout 0.1 to 5 hours to form the extrudate particles. The preferreddiameter of cylindrical extrudate particles is between about 0.7 andabout 3.5 mm, with a length-to-diameter ratio of between about 1:1 and5:1.

[0040] A platinum-group-metal component is an essential ingredient ofthe catalyst. This component comprises platinum, palladium, ruthenium,rhodium, iridium, osmium or mixtures thereof, with platinum beingpreferred. The platinum-group metal may exist within the final catalystas a compound such as an oxide, sulfide, halide, oxyhalide, etc., inchemical combination with one or more of the other ingredients of thecomposite or as an elemental metal. Best results are obtained whensubstantially all of this component is present in the elemental stateand it is homogeneously dispersed within the carrier material. Thiscomponent may be present in the final catalyst composite in any amountwhich is catalytically effective; the platinum-group metal generallywill comprise about 0.01 to about 2 mass-% of the final catalyst,calculated on an elemental basis. Excellent results are obtained whenthe catalyst contains about 0.05 to about 1 mass-% of platinum.

[0041] The platinum-group-metal component may be incorporated in theporous carrier material in any suitable manner, such as coprecipitation,ion-exchange or impregnation. The preferred method of preparing thecatalyst involves the utilization of a soluble, decomposable compound ofplatinum-group metal to impregnate the carrier material in a relativelyuniform manner. For example, the component may be added to the supportby commingling the latter with an aqueous solution of chloroplatinic orchloroiridic or chloropalladic acid. Other water-soluble compounds orcomplexes of platinum-group metals may be employed in impregnatingsolutions and include ammonium chloroplatinate, bromoplatinic acid,platinum trichloride, platinum tetrachloride hydrate, platinumdichlorocarbonyl dichloride, dinitrodiaminoplatinum, sodiumtetranitroplatinate (II), palladium chloride, palladium nitrate,palladium sulfate, diamminepalladium (II) hydroxide, tetramminepalladium(II) chloride, hexamminerhodium chloride, rhodium carbonylchloride,rhodium trichloride hydrate, rhodium nitrate, sodium hexachlororhodate(III), sodium hexanitrorhodate (III), iridium tribromide, iridiumdichloride, iridium tetrachloride, sodium hexanitroiridate (III),potassium or sodium chloroiridate, potassium rhodium oxalate, etc. Theutilization of a platinum, iridium, rhodium, or palladium chloridecompound, such as chloroplatinic, chloroiridic or chloropalladic acid orrhodium trichloride hydrate, is preferred since it facilitates theincorporation of both the platinum-group-metal component and at least aminor quantity of the preferred halogen component in a single step.Hydrogen chloride or the like acid is also generally added to theimpregnation solution in order to further facilitate the incorporationof the halogen component and the uniform distribution of the metalliccomponents throughout the carrier material. In addition, it is generallypreferred to impregnate the carrier material after it has been calcinedin order to minimize the risk of washing away the valuableplatinum-group metal.

[0042] Generally the platinum-group-metal component is dispersedhomogeneously in the catalyst. Dispersion of the platinum-group metalpreferably is determined by Scanning Transmission Electron Microscope(STEM), comparing metals concentrations with overall catalyst metalcontent. In an alternative embodiment one or more platinum-group-metalcomponents may be present as a surface-layer component as described inU.S. Pat. No. 4,677,094, incorporated by reference. The “surface layer”is the layer of a catalyst particle adjacent to the surface of theparticle, and the concentration of surface-layer metal tapers off inprogressing from the surface to the center of the catalyst particle.

[0043] A Group IVA (IUPAC 14) metal component is another essentialingredient of the catalyst of the present invention. Of the Group IVA(IUPAC 14) metals, germanium and tin are preferred and tin is especiallypreferred. This component may be present as an elemental metal, as achemical compound such as the oxide, sulfide, halide, oxychloride, etc.,or as a physical or chemical combination with the porous carriermaterial and/or other components of the catalyst. Preferably, asubstantial portion of the Group IVA (IUPAC 14) metal exists in thefinished catalyst in an oxidation state above that of the elementalmetal. The Group IVA (IUPAC 14) metal component optimally is utilized inan amount sufficient to result in a final catalyst containing about 0.01to about 5 mass % metal, calculated on an elemental basis, with bestresults obtained at a level of about 0.1 to about 2 mass-% metal.

[0044] The Group IVA (IUPAC 14) metal component may be incorporated inthe catalyst in any suitable manner to achieve a homogeneous dispersion,such as by coprecipitation with the porous carrier material,ion-exchange with the carrier material or impregnation of the carriermaterial at any stage in the preparation. One method of incorporatingthe Group IVA (IUPAC 14) metal component into the catalyst compositeinvolves the utilization of a soluble, decomposable compound of a GroupIVA (IUPAC 14) metal to impregnate and disperse the metal throughout theporous carrier material. The Group IVA (IUPAC 14) metal component can beimpregnated either prior to, simultaneously with, or after the othercomponents are added to the carrier material. Thus, the Group IVA (IUPAC14) metal component may be added to the carrier material by comminglingthe latter with an aqueous solution of a suitable metal salt or solublecompound such as stannous bromide, stannous chloride, stannic chloride,stannic chloride pentahydrate; or germanium oxide, germaniumtetraethoxide, germanium tetrachloride; or lead nitrate, lead acetate,lead chlorate and the like compounds. The utilization of Group IVA(IUPAC 14) metal chloride compounds, such as stannic chloride, germaniumtetrachloride or lead chlorate is particularly preferred since itfacilitates the incorporation of both the metal component and at least aminor amount of the preferred halogen component in a single step. Whencombined with hydrogen chloride during the especially preferred aluminapeptization step described hereinabove, a homogeneous dispersion of theGroup IVA (IUPAC 14) metal component is obtained in accordance with thepresent invention. In an alternative embodiment, organic metal compoundssuch as trimethyltin chloride and dimethyltin dichloride areincorporated into the catalyst during the peptization of the inorganicoxide binder, and most preferably during peptization of alumina withhydrogen chloride or nitric acid.

[0045] A lanthanide-series metal component is another essentialcomponent of the present catalyst. Included in the lanthanide series arelanthanum, cerium, praseodymium, neodymium, promethium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium and lutetium; a cerium component is preferred. The lanthanidecomponent may in general be present in the catalyst in any catalyticallyavailable form such as the elemental metal, a compound such as theoxide, hydroxide, halide, oxyhalide, aluminate, or in chemicalcombination with one or more of the other ingredients of the catalyst.Although not intended to so restrict the present invention, it isbelieved that best results are obtained when the lanthanide component ispresent in the composite in a form wherein substantially all of thelanthanide moiety is in an oxidation state above that of the elementalmetal such as in the form of the oxide, oxyhalide or halide or in amixture thereof and the subsequently described oxidation and reductionsteps that are preferably used in the preparation of the instantcatalyst are specifically designed to achieve this end.

[0046] The lanthanide-series metal component is concentrated in thesurface layer of each catalyst particle. In defining the presentinvention, “layer” is a stratum of a catalyst particle of substantiallyuniform thickness at a substantially uniform distance from the surfaceof the catalyst particle. The “surface layer” is the layer of thecatalyst particle adjacent to the surface of the particle. Thesurface-layer concentration is the average of measurements within asurface layer which, for purposes of characterizing the presentinvention, is about 100 microns deep. The concentration of surface-layerlanthanide-group metal tapers off in progressing from the surface to thecenter of the catalyst particle, and is substantially lower in the“central core” of the particle than in its surface layer. “Central core”is defined, in characterizing the present invention, as a core of acatalyst particle representing 50% of the diameter of the particle.“Diameter” is defined as the minimum regular dimension through thecenter of the catalyst particle; for example, this dimension would bethe diameter of the cylinder of an extrudate. For the preferredspherical particles of the present invention, the central core is aspherical portion in the center of the particle having a diameter 50% ofthat of the spherical particle. These definitions do not exclude the useof other quantitative criteria for defining the gradient of metalconcentration in a catalyst particle. In the present invention, however,the surface-layer component is measured as the concentration in thelayer which extends 100 microns from the surface of the particle and thecentral core represents 50% of the diameter of the particle.

[0047] The gradient of the metal promoter preferably is determined byScanning Electron Microscopy (“SEM”). SEM determinations of local metalconcentrations are effected on at least three sample particles from abed of catalyst particles. Samples are selected from the bed bytechniques known to those of ordinary skill in the art. The SEM datashow the approximate metals content of any one point within a catalystparticle, based on the metals distribution profile in relation to thequantity of support. Measurement of the surface-layer concentration iseffected as the average of the concentration in the 100-micron surfacelayer of at least three catalyst particles. The result of each analysismay not be based upon a zero point; attempting to integrate adistribution curve is not possible, and could lead to interpretationerrors as the entire curve could be shifted either up or down. However,the data are useful for making relative comparisons of metaldistributions

[0048] The surface-layer lanthanide-series metal component, incharacterizing the present invention, preferably has a concentration onan elemental basis as measured by SEM in the surface layer of particlesof the catalyst which is at least about twice the concentration of thelanthanide-series metal in the central core of the particles. Morepreferably the metal concentration in the surface layer is at leastabout three times, and optimally about five times or more, theconcentration in the central core of the particles. In an alternativedefinition, about 50% or more of a surface-layer metal is contained inthe surface layer of a catalyst.

[0049] In contrast, a homogeneously dispersed metal component, whilegenerally showing some variation in concentration through a catalystparticle, demonstrates a substantially smaller ratio of metal in thesurface layer to metal in the central core than that characterizing thesurface-layer metal. Measured by SEM, a homogeneously dispersed metalpreferably has a concentration at one stratum on three or more catalystparticles which differs by less than about 50% from the average SEMmetal concentration on the particles.

[0050] The surface-layer lanthanide may be incorporated into thecatalyst particle in any manner suitable to effect a decreasing gradientof the metal from the surface to the center of the particle. One exampleof this would be by spray impregnation. A spray nozzle is located withina rotating drum which holds a catalyst support, and a solution of thesalt of the surface-layer metal is ejected from the nozzle using air toform fine droplets of spray which contact the support in the rotatingdrum for effective mixing. Suitable salts may comprise but are notlimited to the nitrates, sulfates, acetates, chlorides, bromides,iodides, amine complexes, and organometallics such as the alkyl andalkoxide compounds. The volume ratio of solution to support issufficient to effect the desired concentration of surface-layer metal inthe catalyst, and preferably would be from about 0.3 to 1.0.

[0051] Alternatively, a metal component is impregnated as a compound,especially a salt, which decomposes at a pH of about 5 or more. Forexample, the preferred metal is impregnated as a chloride salt whichdecomposes upon contact. Other means, which do not limit the invention,include using a compound of the metal which complexes other componentsor which does not penetrate into the interior of the particle. Anexample is a multi-dentated ligand, such as carboxylic acids or metalcompounds containing amino groups, thiol groups, phosphorus groups orother polar groups which can bond strongly to an oxide support.

[0052] The lanthanide-metal component is incorporated into the catalystin any amount which is catalytically effective, with good resultsobtained with about 0.05 to about 5 mass-% lanthanide on an elementalbasis in the catalyst. Best results are ordinarily achieved with about0.2 to about 2 mass-% lanthanide, calculated on an elemental basis. Thepreferred atomic ratio of lanthanide to platinum-group metal for thiscatalyst is at least about 1.3:1, preferably about 1.5:1 or more, andespecially from about 2:1 to about 5:1.

[0053] Optionally the catalyst may also contain other components ormixtures thereof which act alone or in concert as catalyst modifiers toimprove activity, selectivity or stability. Some known catalystmodifiers include rhenium, cobalt, nickel, iron, tungsten, molybdenum,chromium, bismuth, antimony, zinc, cadmium and copper. Catalyticallyeffective amounts of these components may be added in any suitablemanner to the carrier material during or after its preparation or to thecatalyst before, while or after other components are being incorporated.

[0054] Preferably, however, a metal component of the catalyst consistsessentially of a platinum-group metal, a Group IVA (IUPAC 14) metal anda lanthanide-series metal, and more preferably of platinum, tin andcerium. The ratio of lanthanide-series metal to platinum-group metal isat least about 1.5, preferably about 2 or more, and more preferably atleast about 4 on an atomic basis.

[0055] An optional component of the catalyst, useful in hydrocarbonconversion embodiments of the present invention comprisingdehydrogenation, dehydrocyclization, or hydrogenation reactions, is analkali or alkaline-earth metal component. More precisely, this optionalingredient is selected from the group consisting of the compounds of thealkali metals—cesium, rubidium, potassium, sodium, and lithium—and thecompounds of the alkaline earth metals—calcium, strontium, barium, andmagnesium. Generally, good results are obtained in these embodimentswhen this component constitutes about 0.01 to about 5 mass-% of thecomposite, calculated on an elemental basis. This optional alkali oralkaline earth metal component can be incorporated into the composite inany of the known ways with impregnation with an aqueous solution of asuitable water-soluble, decomposable compound being preferred.

[0056] As heretofore indicated, it is necessary to employ at least oneoxidation step in the preparation of the catalyst. The conditionsemployed to effect the oxidation step are selected to convertsubstantially all of the metallic components within a catalyticcomposite to their corresponding oxide form. The oxidation steptypically takes place at a temperature of from about 370° to about 650°C. An oxygen atmosphere is employed typically comprising air. Generally,the oxidation step will be carried out for a period of from about 0.5 toabout 10 hours or more, the exact period of time being that required toconvert substantially all of the metallic components to theircorresponding oxide form. This time will, of course, vary with theoxidation temperature employed and the oxygen content of the atmosphereemployed.

[0057] In addition to the oxidation step, a halogen adjustment step mayalso be employed in preparing the catalyst. As heretofore indicated, thehalogen adjustment step may serve a dual function. First, the halogenadjustment step may aid in homogeneous dispersion of the Group IVA(IUPAC 14) metal and other metal component. Additionally, the halogenadjustment step can serve as a means of incorporating the desired levelof halogen into the final catalyst. The halogen adjustment step employsa halogen or halogen-containing compound in air or an oxygen atmosphere.Since the preferred halogen for incorporation into the catalystcomprises chlorine, the preferred halogen or halogen-containing compoundutilized during the halogen adjustment step is chlorine, HCl orprecursor of these compounds. In carrying out the halogen adjustmentstep, the catalyst is contacted with the halogen or halogen-containingcompound in air or an oxygen atmosphere at an elevated temperature offrom about 370° to about 650° C. It is further desired to have waterpresent during the contacting step in order to aid in the adjustment. Inparticular, when the halogen component of the catalyst compriseschlorine, it is preferred to use a mole ratio of water to HCl of about5:1 to about 100:1. The duration of the halogenation step is typicallyfrom about 0.5 to about 5 hours or more. Because of the similarity ofconditions, the halogen adjustment step may take place during theoxidation step. Alternatively, the halogen adjustment step may beperformed before or after the oxidation step as required by theparticular method being employed to prepare the catalyst of theinvention. Irrespective of the exact halogen adjustment step employed,the halogen content of the final catalyst should be such that there issufficient halogen to comprise, on an elemental basis, from about 0.1 toabout 10 mass-% of the finished composite.

[0058] In preparing the catalyst, it is also necessary to employ areduction step. The reduction step is designed to reduce substantiallyall of the platinum-group metal component to the corresponding elementalmetallic state and to ensure a relatively uniform and finely divideddispersion of this component throughout the refractory inorganic oxide.It is preferred that the reduction step takes place in a substantiallywater-free environment. Preferably, the reducing gas is substantiallypure, dry hydrogen (i.e., less than 20 volume ppm water). However, otherreducing gases may be employed such as CO, nitrogen, etc. Typically, thereducing gas is contacted with the oxidized catalytic composite atconditions including a reduction temperature of from about 315° to about650° C. for a period of time of from about 0.5 to 10 or more hourseffective to reduce substantially all of the platinum-group-metalcomponent to the elemental metallic state. The reduction step may beperformed prior to loading the catalytic composite into the hydrocarbonconversion zone or it may be performed in situ as part of a hydrocarbonconversion process start-up procedure. However, if this latter techniqueis employed, proper precautions must be taken to predry the conversionunit to a substantially water-free state, and a substantially water-freereducing gas should be employed.

[0059] Optionally, the catalytic composite may be subjected to apresulfiding step. The optional sulfur component may be incorporatedinto the catalyst by any known technique.

[0060] The catalyst of the present invention has particular utility as ahydrocarbon conversion catalyst. The hydrocarbon which is to beconverted is contacted with the catalyst at hydrocarbon-conversionconditions, which include a temperature of from 40° to 300° C., apressure of from atmospheric to 200 atmospheres absolute and liquidhourly space velocities from about 0.1 to 100 hr⁻¹. The catalyst isparticularly suitable for catalytic reforming of gasoline-rangefeedstocks, and also may be used for, inter alia, dehydrocyclization,isomerization of aliphatics and aromatics, dehydrogenation,hydro-cracking, disproportionation, dealkylation, alkylation,transalkylation, and oligomerization.

[0061] The preferred reforming process of the present invention iseffected at conditions including a pressure selected within the range ofabout 100 kPa to 7 MPa (abs). Particularly good results are obtained atlow pressure, namely a pressure of about 350 to 2500 kPa (abs).Reforming temperature is in the range from about 315° to 600° C., andpreferably from about 425° to 565° C. As is well known to those skilledin the reforming art, the initial selection of the temperature withinthis broad range is made primarily as a function of the desired octaneof the product reformate considering the characteristics of the chargestock and of the catalyst. Ordinarily, the temperature then isthereafter slowly increased during the run to compensate for theinevitable deactivation that occurs to provide a constant octaneproduct. Sufficient hydrogen is supplied to provide an amount of about 1to about 20 moles of hydrogen per mole of hydrocarbon feed entering thereforming zone, with excellent results being obtained when about 2 toabout 10 moles of hydrogen are used per mole of hydrocarbon feed.Likewise, the liquid hourly space velocity (LHSV) used in reforming isselected from the range of about 0.1 to about 20 hr⁻¹, with a value inthe range of about 1 to about 5 hr⁻¹ being preferred.

[0062] The hydrocarbon feedstock that is charged to this reformingsystem preferably is a naphtha feedstock comprising naphthenes andparaffins that boil within the gasoline range. The preferred feedstocksare naphthas consisting principally of naphthenes and paraffins,although, in many cases, aromatics also will be present. This preferredclass includes straight-run gasolines, natural gasolines, syntheticgasolines, and the like. As an alternative embodiment, it is frequentlyadvantageous to charge thermally or catalytically cracked gasolines,partially reformed naphthas, or dehydrogenated naphthas. Mixtures ofstraight-run and cracked gasoline-range naphthas can also be used toadvantage. The gasoline-range naphtha charge stock may be a full-boilinggasoline having an initial ASTM D-86 boiling point of from about 40-80°C. and an end boiling point within the range of from about 160-220° C.,or may be a selected fraction thereof which generally will be ahigher-boiling fraction commonly referred to as a heavy naphtha—forexample, a naphtha boiling in the range of 100-200° C. If the reformingis directed to production of one or more of benzene, toluene andxylenes, the boiling range may be principally or substantially withinthe range of 60°-150° C. In some cases, it is also advantageous toprocess pure hydrocarbons or mixtures of hydrocarbons that have beenrecovered from extraction units—for example, raffinates from aromaticsextraction or straight-chain paraffins—which are to be converted toaromatics.

[0063] It is generally preferred to utilize the present invention in asubstantially water-free environment. Essential to the achievement ofthis condition in the reforming zone is the control of the water levelpresent in the feedstock and the hydrogen stream which is being chargedto the zone. Best results are ordinarily obtained when the total amountof water entering the conversion zone from any source is held to a levelless than 50 ppm and preferably less than 20 ppm, expressed as weight ofequivalent water in the feedstock. In general, this can be accomplishedby careful control of the water present in the feedstock and in thehydrogen stream. The feedstock can be dried by using any suitable dryingmeans known to the art. For example, the water content of the feedstockmay be adjusted by suitable stripping operations in a fractionationcolumn or like device. Alternatively or in addition, water may beremoved using a conventional solid adsorbent having a high selectivityfor water; for instance, sodium or calcium crystalline aluminosilicates,silica gel, activated alumina, molecular sieves, anhydrous calciumsulfate, high surface area sodium, and the like. In some cases, acombination of adsorbent drying and distillation drying may be usedadvantageously to effect almost complete removal of water from thefeedstock.

[0064] It is preferred to maintain the water content of the hydrogenstream entering the hydrocarbon conversion zone at a level of about 10to about 20 volume ppm or less. In the cases where the water content ofthe hydrogen stream is above this range, this can be convenientlyaccomplished by contacting the hydrogen stream with a suitable desiccantsuch as those mentioned above at conventional drying conditions.

[0065] It is a preferred practice to use the present invention in asubstantially sulfur-free environment. Any control means known in theart may be used to treat the naphtha feedstock which is to be charged tothe reforming reaction zone. For example, the feedstock may be subjectedto adsorption processes, catalytic processes, or combinations thereof.Adsorption processes may employ molecular sieves, high surface areasilica-aluminas, carbon molecular sieves, crystalline aluminosilicates,activated carbons, high surface area metallic containing compositions,such as nickel or copper and the like. It is preferred that thesefeedstocks be treated by conventional catalytic pretreatment methodssuch as hydrorefining, hydrotreating, hydrodesulfurization, etc., toremove substantially all sulfurous, nitrogenous and water-yieldingcontaminants therefrom, and to saturate any olefins that may becontained therein. Catalytic processes may employ traditional sulfurreducing catalysts known to the art including refractory inorganic oxidesupports containing metals selected from the group comprising GroupVI-B(6), Group II-B(12), and Group VIII (IUPAC 8-10) of the PeriodicTable.

[0066] In the preferred catalytic reforming embodiment, hydrocarbonfeedstock and a hydrogen-rich gas are preheated and charged to areforming zone containing typically two to five reactors in series.Suitable heating means are provided between reactors to compensate forthe net endothermic heat of reaction in each of the reactors. Reactantsmay contact the catalyst in individual reactors in either upflow,downflow, or radial flow fashion, with the radial flow mode beingpreferred. The catalyst is contained in a fixed-bed system or,preferably, in a moving-bed system with associated continuous catalystregeneration. Alternative approaches to reactivation of deactivatedcatalyst are well known to those skilled in the art, and includesemiregenerative operation in which the entire unit is shut down forcatalyst regeneration and reactivation or swing-reactor operation inwhich an individual reactor is isolated from the system, regenerated andreactivated while the other reactors remain on-stream. The preferredcontinuous catalyst regeneration in conjunction with a moving-bed systemis disclosed, inter alia, in U.S. Pat. Nos. 3,647,680; 3,652,231;3,692,496; and 4,832,291, all of which are incorporated herein byreference.

[0067] Effluent from the reforming zone is passed through a coolingmeans to a separation zone, typically maintained at about 0° to 65° C.,wherein a hydrogen-rich gas is separated from a liquid stream commonlycalled “unstabilized reformate”. The resultant hydrogen stream can thenbe recycled through suitable compressing means back to the reformingzone. The liquid phase from the separation zone is typically withdrawnand processed in a fractionating system in order to adjust the butaneconcentration, thereby controlling front-end volatility of the resultingreformate.

EXAMPLES

[0068] The following examples are presented to elucidate the catalystand process of the present invention and demonstrate performancerelative to the art. These examples are offered as illustrativeembodiments and should not be interpreted as limiting the claims.

Example I

[0069] The feedstock on which catalyst comparisons were based was anessentially sulfur-free naphtha having characteristics as follows: Sp.gr. 0.736 ASTM D-86,° C.: IBP 83 10% 93 50% 112 90% 136 EP 161 Mass-%Paraffins 60.4 Naphthenes 26.7 Aromatics 12.9

[0070] Catalytic reforming tests were performed on the above naphthafeedstock using catalysts of the invention in comparison with catalystsof the known art.

Example II

[0071] A spherical catalyst comprising platinum, tin and cerium onalumina was prepared to demonstrate the features of the invention. Tinwas incorporated into alumina sol according to the known art, and thetin-containing alumina sol was oil-dropped to form 1.6 mm spheres whichwere steamed to dryness at about 10% LOI and calcined at 650° C. Thespherical support then was impregnated with aqueous cerium nitrate at asolution-to-base ratio of 0.45:1 and calcined at 350° C. for 2 hours,impregnated with chloroplatinic acid in 2% HCl, dried and oxychlorinatedat 525° C. followed by reduction with pure hydrogen at 565° C.

[0072] The finished catalyst of the invention was designated as CatalystA, contained about 1.3 mass-% chloride and had the following approximatemetals contents as mass-% of the elemental metal: Platinum 0.38 Tin 0.3Cerium 0.25

Example III

[0073] A spherical catalyst of the known art comprising platinum, tinand cerium on alumina was prepared as a control relative to theinvention. Tin was incorporated into a spherical alumina supportaccording to the known art as described in Example II. The sphericalsupport then was impregnated with aqueous 3.5 mass-% cerium nitrate at asolution-to-base ratio of 1:1 and oxychlorinated at 525° C. for 2 hours,impregnated with chloroplatinic acid in 2% HCl, dried and oxychlorinatedat 525° C. followed by reduction with pure hydrogen at 565° C.

[0074] The finished control was designated Catalyst B, contained about1.4 mass-% chloride, and had the following approximate metals contentsas mass-% of the elemental metal: Platinum 0.37 Tin 0.3 Cerium 0.97

Example IV

[0075] A second control catalyst of the known art was preparedcomprising platinum and tin on alumina was prepared for comparison tothe invention. Tin was incorporated into a spherical alumina supportaccording to the known art as described in Example II. The sphericalsupport then was impregnated with chloroplatinic acid in 2% HCl, driedand oxychlorinated at 525° C. followed by reduction with pure hydrogenat 565° C. The second control was designated Catalyst C and had thefollowing approximate metals contents as mass-% of the elemental metal:Platinum 0.37 Tin 0.3

Example V

[0076] Catalysts A and B were evaluated by Scanning Election Microscopy(SEM). The purpose of this analysis was to identify the relativedistribution of cerium across the radius of the catalyst particles.Three particles each of Catalysts A and B were evaluated in order toprovide reliable average data.

[0077] The SEM data shows the approximate metals content of any onepoint within the catalyst pill, as indicated hereinabove, based on themetals distribution profile in relation to the support. The data areuseful for making relative comparisons of metal distributions.

[0078]FIG. 1 shows the relative distribution of the cerium concentrationacross the 800-micron radius of particles of Catalyst A from the surfaceto the center of each particle. Catalyst A displayed an exceptionallyhigh concentration of cerium on a relative basis in the surface layer ofthe catalyst particles. Since there was virtually no cerium identifiedin any layer beyond the 100-micron surface layer, the concentration ofcerium in the 100-micron surface layer was at least several times higherthan in the central core representing 50% of the diameter of thecatalyst.

[0079] In contrast, the cerium concentration in the 100-micron surfacelayer of Catalyst B differed by no more than about 10-20% from theconcentration in the central core.

Example VI

[0080] Pilot-plant tests were structured to compare the activity andselectivity of Catalyst A of the invention with Catalysts B and C of theknown art in the catalytic reforming of a feedstock as described inExample I.

[0081] Each test was based on reforming conditions comprising a pressureof 0.8 MPa (abs), a liquid hourly space velocity of 3 hr⁻¹, and ahydrogen/hydrocarbon ratio of 8. A range of conversion was studied byvarying temperature to provide data points for each catalyst at 502° C.,512° C., 522° C., and 532° C.

[0082]FIG. 2 compares the activity of Catalysts A, B and C over theabove temperature range. Activity of the cerium-containing catalysts,determined as the temperature requirement for a given conversion, wasless favorable at low conversions and somewhat more favorable at highconversions relative to Catalyst C of the known art. Catalyst A of theinvention generally showed an activity advantage over Catalyst B of theknown art.

[0083]FIG. 3 compares the selectivity, measured as mass-% C₅+ yield, ofCatalysts A, B and C. Both of the cerium-containing catalysts A and Bshowed a selectivity advantage over the control Catalyst C. Catalyst Bdemonstrated higher selectivity; however, Catalyst A of the inventionobtained about 50-80% of this selectivity advantage with about ¼ of thecontent of cerium, which contributes significantly to catalyst cost, incomparison to Catalyst B(0.25 vs. 0.97 mass-%, respectively). Example II

Example VII

[0084] Another spherical catalyst comprising platinum, tin and cerium onalumina was prepared to demonstrate the features of the invention. Tinwas incorporated into alumina sol according to the known art, and thetin-containing alumina sol was oil-dropped to form 1.6 mm spheres whichwere calcined at 650° C. The spherical support then was impregnated withchloroplatinic acid, steam calcined at 525° C., impregnated with ceriumnitrate in deionized water, dried and oxychlorinated at 525° C. followedby reduction with pure hydrogen at 565° C.

[0085] The finished catalyst of the invention was designated as CatalystD, contained about 1.3 mass-% chloride and had the following approximatemetals contents as mass-% of the elemental metal: Platinum 0.3 Tin 0.3Cerium 0.94

Example VIII

[0086] A spherical catalyst of the known art comprising platinum, tinand cerium on alumina was prepared as a control relative to Catalyst Dof the invention. Tin was incorporated into a spherical alumina supportaccording to the known art. The spherical support then was impregnatedwith chloroplatinic acid, steam calcined at 525° C., impregnated withcerium nitrate in 2 mass-% HCl, dried and oxychlorinated at 525° C.followed by reduction with pure hydrogen at 565° C.

[0087] The finished control was designated Catalyst E, contained about1.3 mass-% chloride, and had the following approximate metals contentsas mass-% of the elemental metal: Platinum 0.3 Tin 0.3 Cerium 0.95

Example IX

[0088] Catalysts D and E were evaluated by Scanning Electron Microscopy(SEM). The purpose of this analysis was to identify the relativedistribution of cerium across the radius of the catalyst particles.Three particles each of Catalysts D and E were evaluated in order toprovide reliable average data.

[0089] The SEM data shows the approximate metals content of any onepoint within the catalyst pill, as indicated hereinabove, based on themetals distribution profile in relation to the support. The data areuseful for making relative comparisons of metal distributions.

[0090]FIG. 4 shows the relative distribution of the cerium concentrationacross the 800-micron radius of particles of Catalyst D from the surfaceto the center of each particle. Catalyst D displayed an exceptionallyhigh concentration of cerium on a relative basis in the surface layer ofthe catalyst particles. The concentration of cerium in the 100-micronsurface layer was at least an order of magnitude higher than in thecentral core representing 50% of the diameter of the catalyst.

[0091] In contrast, the cerium concentration in the 100-micron surfacelayer of Catalyst E differed by no more than about 20% from theconcentration in the central core.

Example X

[0092] Pilot-plant tests were structured to compare the activity andselectivity of Catalyst D of the invention with Catalyst E of the knownart in the catalytic reforming of a feedstock having the followingcharacteristics: Sp. gr. 0.753 ASTM D-86,° C.: IBP 89 50% 105 EP 182Mass-% Paraffins 59 Naphthenes 26 Aromatics 15

[0093] Each test was based on reforming conditions comprising a pressureof 0.8 MPa (abs), a liquid hourly space velocity of 3 hr⁻¹, and ahydrogen/hydrocarbon ratio of 2. The operating temperature wasestablished as that necessary to obtain a C₅+ product having a Researchoctane number of 102 clear.

[0094] The catalysts showed the following comparative performance:Catalyst D Catalyst E Temperature required, ° C. 518 516 C₅₊ yield,mass-% 88.5 87.6

[0095] Catalyst D of the invention thus was 2° C. less active than thecontrol, but showed a significant selectivity advantage of 0.9 mass-%.

Example XI

[0096] A composite comprising tin and surface cerium on alumina wasprepared to demonstrate the features of the invention. Tin wasincorporated into alumina sol according to the known art, and thetin-containing alumina sol was oil-dropped to form 1.6 mm spheres. Thespherical support then was impregnated with aqueous cerium nitrate at asolution-to-base ratio of 0.45:1 and was oxychlorinated at 525° C. for 2hours and dried at 525° C. The composite was designated as Composite Xand contained about 1 mass-% chloride and 0.15 mass-% cerium expressedas content of the elemental metal.

Example XII

[0097] A composite comprising tin and surface lanthanum on alumina wasprepared to demonstrate the features of the invention. Tin wasincorporated into alumina sol according to the known art, and thetin-containing alumina sol was oil-dropped to form 1.6 mm spheres. Thespherical support then was impregnated with aqueous lanthanum nitrate ata solution-to-base ratio of 0.45:1 and were oxychlorinated at 525° C.for 2 hours and dried at 525° C. The composite was designated asComposite Y and contained about 1 mass-% chloride and 0.15 mass-%lanthanum expressed as content of the elemental metal.

Example XIII

[0098] Composites X and Y were evaluated by Scanning Electron Microscopy(SEM). The purpose of this analysis was to identify the relativedistribution of tin and cerium across the radius of the catalystparticles. Three particles each of Catalysts A and B were evaluated inorder to provide reliable average data.

[0099] The SEM data shows the approximate metals content of any onepoint within the catalyst pill, as indicated hereinabove, based on themetals distribution profile in relation to the support. The data areuseful for making relative comparisons of metal distributions.

[0100]FIG. 5 shows the relative distribution of the cerium and tinconcentration across the 800-micron radius of particles of Composite Xfrom the surface to the center of each particle. Composite X displayedan exceptionally high concentration of cerium on a relative basis in thesurface layer of the catalyst particles. The concentration of cerium inthe 100-micron surface layer was about an order of magnitude (10 times)or more higher than in the central core representing 50% of the diameterof the catalyst.

[0101] In contrast, the tin concentration showed no clear pattern awayfrom uniform dispersion across the layers of the composite.

[0102]FIG. 6 shows the relative distribution of the lanthanum and tinconcentration across the 800-micron radius of particles of Composite Yfrom the surface to the center of each particle. Composite Y displayedan exceptionally high concentration of lanthanum on a relative basis inthe surface layer of the catalyst particles. The concentration oflanthanum in the 100-micron surface layer was about 4-6 times higherthan in the central core representing 50% of the diameter of thecatalyst.

[0103] In contrast, the tin concentration showed no clear pattern awayfrom uniform dispersion across the layers of the composite.

Example XIV

[0104] Composites X and Y were ground to 40-60 mesh particles along witha control comprising the base before platinum addition of Catalyst C,here designated Composite Z. The three composites were testedcomparatively in the conversion of 1-heptene, a measure of aluminaactivity, at a temperature of 425° C. and atmospheric pressure (13 torr1-heptene, balance H₂) over a range of gas hourly space velocities(GHSV).

[0105] Conversion of heptene over the three composites is compared inFIG. 7 as a function of GHSV. Composite X comprising cerium demonstratedthe highest activity, with Composite Y generally showing equivalent orhigher activity than the control.

[0106]FIG. 8 compares mass-% selectivity to naphthenes and aromaticsrelated to heptene conversion. Composites X and Y of the invention bothshowed higher selectivity than the control, with Composite Ydemonstrating the highest selectivity.

We claim:
 1. A catalyst useful in catalytic reforming having a particlediameter of between about 0.7 and about 3.5 mm and comprising acombination of a refractory inorganic oxide support with amultimetallic, multigradient metal component comprising about
 0. 01 to 2mass-% on an elemental basis of a homogeneously dispersedplatinum-group-metal component, about 0.01 to 5 mass-% on an elementalbasis of a homogeneously dispersed Group IVA (IUPAC 14) metal componentand about 0.05 to 5 mass-% on an elemental basis of a surface-layercerium component.
 2. The catalyst of claim 1 wherein the concentrationof the cerium component in a 100-micron surface layer of particles ofthe catalyst is at least about twice the concentration of the ceriumcomponent in the central core of the particles.
 3. The catalyst of claim2 wherein the concentration of the cerium component in a 100-micronsurface layer of particles of the catalyst is at least about three timesthe concentration of the cerium component in the central core of theparticles.
 4. The catalyst of claim 1 wherein the platinum-group-metalcomponent comprises a platinum component.
 5. The catalyst of claim 1wherein the Group IVA (IUPAC 14) metal component comprises a tincomponent.
 6. The catalyst of claim 1 wherein the multigradient metalcomponent consists essentially of components of platinum, tin andcerium.
 7. The catalyst of claim 1 wherein the atomic ratio of cerium toplatinum-group metal is at least about 1.3 on an elemental basis.
 8. Thecatalyst of claim 1 wherein the refractory inorganic oxide comprisesalumina.
 9. The catalyst of claim 1 further comprising from about 0.1 to10 mass-% on an elemental basis of a halogen component.
 10. The catalystof claim 9 wherein the halogen component comprises a chlorine component.11. A method of preparing a catalyst suitable for the reforming ofhydrocarbons comprising: (a) forming a catalyst support comprising arefractory inorganic oxide and having a particle diameter of betweenabout 0.7 and about 3.5 mm; (b) incorporating a homogeneously disperseddistributed Group IVA (IUPAC 14) metal component, a homogeneouslydistributed platinum-group metal component and a surface-layer ceriumcomponent into the support to form a catalyst composite; and (c)finishing the composite to form a catalyst by one or both of calcinationand reduction.